Uptake and localization of 3H-retinol and 3H-retinoic acid by Y-79 human retinoblastoma cells in culture were studied. Specific binding proteins ("receptors") for both retinoids were observed in the cytoplasm but only 3H-retinoic acid was bound and specifically compartmentalized in cell nuclei. Thus retinoic acid (a normal vitamin A metabolite) may act in the nucleus at the genetic level in these cells while retinol appears to play a role in the cytoplasm, perhaps in glycoprotein biosynthesis. Retinoid receptors are also found in other ocular tissues (e.g. pigment epithelium) where they appear to mediate the action of retinoids.